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How Does a Race Car Master Cylinder Work? - Motorsport Tech Session

American Government Special Collections Reference Desk

How Does a Race Car Master Cylinder Work? - Motorsport Tech Session

Grant Loc
July 6, 2011

Hello, I trust this article has found you healthy, happy and enjoying your Motorsports.

Over the years I have been asked questions about all sorts of Motorsport related problems and how things work. One of these questions keeps popping up so I thought it was time to put it down in an article.

Today I would like to give you some information explaining how a master cylinder works.

The Master Cylinder is basically a hydraulic cylinder that when a force is applied to one end that is connected to a sliding piston. This force applied to the piston creates pressure in the cylinder and forces brake fluid out of an outlet.

This is how a single piston or single reservoir master cylinder operates:

The push rod forces the piston forward in the cylinder bore. The sealing mechanism ahead of the piston is called the primary cup, and as it travels down the cylinder bore it closes the compensating port so that the hydraulic system is completely sealed.

As forces are increased on the push rod, the fluid ahead of the primary cup continues to build up in pressure and begins to flow around the residual pressure check valve and into the hydraulic brake lines. This pressure is then transmitted to the individual wheels, actuating the brakes.

When the brake pedal is released, the return springs on the brake shoes / callipers force the fluid back to the hydraulic lines, around the residual check valve and into the cylinder bore. The piston is forced back toward the boot end of the master cylinder, opening up the compensating port allowing fluid to return to the reservoir.

New master cylinders should be checked thoroughly, the master cylinder should be part of a frequent maintenance check, with a tear-down and inspection and rebuild if necessary. Be sure to check the condition of the piston seal.

Spongy Brake Pedal

If you experience a spongy brake pedal and you have faithfully bled the brake system and you still have a spongy pedal like air is trapped in the system. I have a few suggestions for you that may solve the problem.

1) Leaks in the system, check the total system for leaks

2) Worn wheel or master cylinder seals

3) Insufficient fluid in the master cylinder

4) The brake fluid is boiling at some point in the brake system

Thank you for your time.

Grant Loc has been involved with Motorsports for over 15 years and the Director of obp Ltd. obp Ltd is a major player in Manufacture and Supply of Quality Race Car Products and provides most of the leading Motorsport distributors all over the World. obp manufacture Race Pedal Boxes, Handbrakes, Alloy Dry Oil Sump Tanks, etc. www.obpltd.com

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